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The Top 20 Most-Cited Papers from 2022 to 2023
2024 Vol. 39, No. 5
Display Method:
2024, 39(5): 1-7.
doi: 10.3724/j.gjgS24050101
Abstract
PDF (11107KB)
Abstract:
One of the strategies for decarbonizing the construction industry is to enhance the efficiency of engineering design in order to minimize the demand for building materials. Recent advancements in the production of high-strength steel have enabled this possibility. The effective utilization of high strength steel in engineering structures can decrease the dimensions of components and the usage amount of steel, consequently leading to reduced manufacturing, transportation, and construction expenses, which aids in resource conservation and contributes to the reduction of carbon emissions. Compared to the ordinary carbon steel Q355, the Q690 high strength steel exhibits excellent strength to self-weight ratios despite its high yield-to-tensile strength ratio and low elongations at fracture. The properties of high strength steel Q690 can greatly influence structural performance. Therefore, it is crucial to quantify the impact of these properties on structural performance in order to determine their suitability for use in building structures. The calculation method for the overall buckling bearing capacity of axial compression members in the current main structural steel design codes is primarily based on research data for ordinary carbon steels Q235 and Q355, and their applicability to Q690 high strength steel needs to be further verified. So it is very necessary to check the applicability of these design methods for axial compression members made of Q690 high strength steel using various fabrication processes. To investigate the overall buckling of cold-formed square columns made of Q690 high strength steel under axial compression, a total of eight specimens were designed. These specimens included four different cross-sectional sizes and eight slenderness ratios. The plate thicknesses used were 6 mm and 10 mm. The overall buckling of these specimens was examined through axial compression tests. Prior to the tests, measurements were taken to determine the geometrical initial bending, load initial eccentricity, and longitudinal residual stress distribution of the sections. Residual stress measurements revealed large residual tensile strain on both the inner and outer surfaces at the welded seams of the cold-formed square section. Additionally, significant residual tensile and compressive strains were found at the outer and the inner surfaces respectively of the round corners of section. It was found that all specimens exhibited overall buckling as the primary mode of failure under axial compression. The test results were compared with the calculation results of Chinese code GB 50017—2017 and European code Eurocode 3. The results indicate that the calculation results based on the design curves suggested by the Chinese code and Eurocode are conservative, and the Chinese code being more conservative compared to the European code. Based on the comparison of test results and design curves in the design code, it is recommended to use the column curve a in GB 50017—2017 and Eurocode 3 for the design of Q690 high strength steel cold-formed square tube columns.
One of the strategies for decarbonizing the construction industry is to enhance the efficiency of engineering design in order to minimize the demand for building materials. Recent advancements in the production of high-strength steel have enabled this possibility. The effective utilization of high strength steel in engineering structures can decrease the dimensions of components and the usage amount of steel, consequently leading to reduced manufacturing, transportation, and construction expenses, which aids in resource conservation and contributes to the reduction of carbon emissions. Compared to the ordinary carbon steel Q355, the Q690 high strength steel exhibits excellent strength to self-weight ratios despite its high yield-to-tensile strength ratio and low elongations at fracture. The properties of high strength steel Q690 can greatly influence structural performance. Therefore, it is crucial to quantify the impact of these properties on structural performance in order to determine their suitability for use in building structures. The calculation method for the overall buckling bearing capacity of axial compression members in the current main structural steel design codes is primarily based on research data for ordinary carbon steels Q235 and Q355, and their applicability to Q690 high strength steel needs to be further verified. So it is very necessary to check the applicability of these design methods for axial compression members made of Q690 high strength steel using various fabrication processes. To investigate the overall buckling of cold-formed square columns made of Q690 high strength steel under axial compression, a total of eight specimens were designed. These specimens included four different cross-sectional sizes and eight slenderness ratios. The plate thicknesses used were 6 mm and 10 mm. The overall buckling of these specimens was examined through axial compression tests. Prior to the tests, measurements were taken to determine the geometrical initial bending, load initial eccentricity, and longitudinal residual stress distribution of the sections. Residual stress measurements revealed large residual tensile strain on both the inner and outer surfaces at the welded seams of the cold-formed square section. Additionally, significant residual tensile and compressive strains were found at the outer and the inner surfaces respectively of the round corners of section. It was found that all specimens exhibited overall buckling as the primary mode of failure under axial compression. The test results were compared with the calculation results of Chinese code GB 50017—2017 and European code Eurocode 3. The results indicate that the calculation results based on the design curves suggested by the Chinese code and Eurocode are conservative, and the Chinese code being more conservative compared to the European code. Based on the comparison of test results and design curves in the design code, it is recommended to use the column curve a in GB 50017—2017 and Eurocode 3 for the design of Q690 high strength steel cold-formed square tube columns.
2024, 39(5): 8-16.
doi: 10.13206/j.gjgS24050102
Abstract:
The application of high strength steels (HSS) in building structures can effectively reduce the consumption of structural steel and erection cost, lower the carbon footprints of building structures, and promote the high-quality development of the construction industry. As one of the most commonly used connection types in steel structures, the slip critical connection transfers the load through the friction forces between the faying surfaces of the connected plates, and is characterized by high rigidity and excellent performances against fatigue and vibrational loadings. So the slip critical connection is commonly used in bridges. In real projects, HSS slip critical connection faces the corrosion problems and low assembly accuracy in site construction. These problems can be solved by thermal spay of aluminum on connecting surfaces and hole reaming. Therefore, the anti-slip performance of HSS slip critical connections after thermal spay of aluminum and reaming has a crucial influence on the shear capacity of the connections. To investigate the anti-slip performance of aluminum-based metalized faying surfaces with high strength bolts of Q690 HSS with different bolt hole types, standard tests and pretension loss tests were carried out. Specimen surfaces were prepared by grit blasting and thermal spray of aluminum after grit blasting. Four bolt hole types were considered for metalized faying surface specimens, including standard holes, oversized holes, long slotted holes perpendicular and parallel to the loading direction, while only the standard hole was considered in the grit blasted group. When the specimens reached the slip load, failure occurred and significant slip was observed. The failure mode of the anti-slip specimens after grit blasting was the surface abrasion around bolt holes, while the failure modes of the anti-slip specimens after thermal spray of aluminum were the abrasion and peeling of coating around bolt holes. Test results indicated that the recommended values of anti-slip coefficient for Q690 HSS grit blasted and metalized faying surfaces connections were 0.50 and 0.60, respectively, and metalized faying surfaces specimens showed excellent slip resistant performance with high resistance and stable behavior; the loss of pretension at 100 h of metalized faying surfaces connections varied from 1.9% to 2.9%; the mean shape factors of Q690 HSS aluminum-based metalized surfaces connections with oversized holes, long slotted holes perpendicular and parallel to the loading direction were 0.98, 0.89 and 0.82, and the minimum shape factors were 0.93, 0.83 and 0.77, respectively, all higher than the specified values in current codes, and designs based on codes specified values got conservative results.
The application of high strength steels (HSS) in building structures can effectively reduce the consumption of structural steel and erection cost, lower the carbon footprints of building structures, and promote the high-quality development of the construction industry. As one of the most commonly used connection types in steel structures, the slip critical connection transfers the load through the friction forces between the faying surfaces of the connected plates, and is characterized by high rigidity and excellent performances against fatigue and vibrational loadings. So the slip critical connection is commonly used in bridges. In real projects, HSS slip critical connection faces the corrosion problems and low assembly accuracy in site construction. These problems can be solved by thermal spay of aluminum on connecting surfaces and hole reaming. Therefore, the anti-slip performance of HSS slip critical connections after thermal spay of aluminum and reaming has a crucial influence on the shear capacity of the connections. To investigate the anti-slip performance of aluminum-based metalized faying surfaces with high strength bolts of Q690 HSS with different bolt hole types, standard tests and pretension loss tests were carried out. Specimen surfaces were prepared by grit blasting and thermal spray of aluminum after grit blasting. Four bolt hole types were considered for metalized faying surface specimens, including standard holes, oversized holes, long slotted holes perpendicular and parallel to the loading direction, while only the standard hole was considered in the grit blasted group. When the specimens reached the slip load, failure occurred and significant slip was observed. The failure mode of the anti-slip specimens after grit blasting was the surface abrasion around bolt holes, while the failure modes of the anti-slip specimens after thermal spray of aluminum were the abrasion and peeling of coating around bolt holes. Test results indicated that the recommended values of anti-slip coefficient for Q690 HSS grit blasted and metalized faying surfaces connections were 0.50 and 0.60, respectively, and metalized faying surfaces specimens showed excellent slip resistant performance with high resistance and stable behavior; the loss of pretension at 100 h of metalized faying surfaces connections varied from 1.9% to 2.9%; the mean shape factors of Q690 HSS aluminum-based metalized surfaces connections with oversized holes, long slotted holes perpendicular and parallel to the loading direction were 0.98, 0.89 and 0.82, and the minimum shape factors were 0.93, 0.83 and 0.77, respectively, all higher than the specified values in current codes, and designs based on codes specified values got conservative results.
2024, 39(5): 17-26.
doi: 10.13206/j.gjgS24050103
Abstract:
A comprehensive investigation into the mechanical properties of 50 and 70 mm thick plates of Q690 high strength steel and their butt-welded sections under tension was presented in this paper, and a total of 40 tensile tests were conducted. Firstly, a total of 18 proportional coupons with circular cross-sections were extracted at three different layers within the plate thicknesses. Tensile tests on all of these coupons were carried out to obtain their mechanical properties, and their variations across the plate thicknesses were also examined. Secondly, submerged arc welding was adopted to prepare butt-welded sections between these thick steel plates with various heat input energy. Micrograpic examinations on typical heat-affected zones of the welded sections were also performed. Standard tensile tests on a total of 22 proportional coupons with rectangular cross-sections were carried out to obtain their mechanical properties, and the full range deformation characteristics of these coupons were assessed and compared, in particular, their tensile strengths and elongations at fracture. Based on the tests on the base metal, it was found that there was only a negligible difference in the mechanical properties of the coupons from different layers of the Q690 50 mm thick steel plate, and it can be concluded that the mechanical properties of the 50 mm plate are homogeneous along the thickness direction. The yield strength and tensile strength of the coupons from the middle layer of the 70 mm plate, compared with the specimens in the upper and lower layers, possess a 7% and 6% reduction, while no reduction of elongation after fracture is found. The tests of welded sections show that, compared with these 16 mm thick plates, the influence of heat input energy on the mechanical properties of these 50 and 70 mm thick plates is small: with the increase of heat input energy from 1.0 to 2.0 kJ/ mm, the reduction of the tensile strength of coupons from 16 mm thick welded sections increased from 0% to 8%; While for the 50 and 70 mm plates, with the increase of heat input energy from 2.4 to 5.0 kJ/ mm, the reductions of tensile strengths maintained to be 4% and 1%. It is obvious that for the thick plate, the effect of increasing heat input energy on the reduction of the mechanical properties is smaller. Therefore, a larger heat input energy is allowed to improve the welding efficiency.
A comprehensive investigation into the mechanical properties of 50 and 70 mm thick plates of Q690 high strength steel and their butt-welded sections under tension was presented in this paper, and a total of 40 tensile tests were conducted. Firstly, a total of 18 proportional coupons with circular cross-sections were extracted at three different layers within the plate thicknesses. Tensile tests on all of these coupons were carried out to obtain their mechanical properties, and their variations across the plate thicknesses were also examined. Secondly, submerged arc welding was adopted to prepare butt-welded sections between these thick steel plates with various heat input energy. Micrograpic examinations on typical heat-affected zones of the welded sections were also performed. Standard tensile tests on a total of 22 proportional coupons with rectangular cross-sections were carried out to obtain their mechanical properties, and the full range deformation characteristics of these coupons were assessed and compared, in particular, their tensile strengths and elongations at fracture. Based on the tests on the base metal, it was found that there was only a negligible difference in the mechanical properties of the coupons from different layers of the Q690 50 mm thick steel plate, and it can be concluded that the mechanical properties of the 50 mm plate are homogeneous along the thickness direction. The yield strength and tensile strength of the coupons from the middle layer of the 70 mm plate, compared with the specimens in the upper and lower layers, possess a 7% and 6% reduction, while no reduction of elongation after fracture is found. The tests of welded sections show that, compared with these 16 mm thick plates, the influence of heat input energy on the mechanical properties of these 50 and 70 mm thick plates is small: with the increase of heat input energy from 1.0 to 2.0 kJ/ mm, the reduction of the tensile strength of coupons from 16 mm thick welded sections increased from 0% to 8%; While for the 50 and 70 mm plates, with the increase of heat input energy from 2.4 to 5.0 kJ/ mm, the reductions of tensile strengths maintained to be 4% and 1%. It is obvious that for the thick plate, the effect of increasing heat input energy on the reduction of the mechanical properties is smaller. Therefore, a larger heat input energy is allowed to improve the welding efficiency.
2024, 39(5): 27-33.
doi: 10.13206/j.gjgS24050104
Abstract:
High strength steel with nominal yield strength, fy, no smaller than 460 MPa has been progressively applied in buildings and bridges due to its good material properties. Compared with normal strength steel, high strength steels have higher yield strength which may reduce the size and dimension of members. In addition, the thinner steel plates may help avoid welding problems associated with thick steel plates as reducing the amount of welding work and improving the welding quality. Fatigue damage is one of the most critical service problems of steel bridge structures. There is no special design standard for fatigue performance of high strength steels in the current design code. This paper presents an experimental investigation on fatigue performance of Q690 high strength steels and their welded sections to determine the fatigue strength, so as to promoto the application of Q690 high strength steel in practical engineering. The monotonic tensile tests were carried out on Q690 high strength steels and their welded sections to examine the material properties. The welded section was etched before test to distinguish the position of base metal, heat affected zone and welded metal during testing, and determined the position of necking was heat affected zone. The various applied loadings of fatigue tests were determined according to the mechanical properties examined in the tensile test, and a series of high-cycle-low-strain cyclic tests on smooth cylindrical coupons had been conducted to determine the S-N curves for Q690 high strength steels and their welded sections. The fatigue limit of Q690 welded sections is 420 MPa, and that of base plate is 668. 8 MPa. It means that the fatigue performance of Q690 welded sections is worse than that of Q690 base plate, while the fatigue resistance of both the Q690 base plate and their welded sections are significantly larger than those given in Eurocode (base plate: 118 MPa, welded section: 82.5 MPa). The hardness test was conducted on the Q690 welded section to determine its hardness distribution along the longitudinal direction. It is found that the weld metal exhibits the larger hardness value as 328 HV, while the softening was identified in the heat affected zone with a hardness of 240 HV, which indicated that the hardness distribution of Q690 welded section is uneven and the difference is significant. Based on the results of etching tests and SEM observations on the fracture surfaces under fatigue loadings, it is found that the crack initiated at the fusion zone rather than the heat affected zone. What’s more, non-metallic inclusions have been identified in the fracture surfaces of Q690 welded sections, it means that the initial imperfections may be a critical parameter affecting the fatigue performance of Q690 welded sections.
High strength steel with nominal yield strength, fy, no smaller than 460 MPa has been progressively applied in buildings and bridges due to its good material properties. Compared with normal strength steel, high strength steels have higher yield strength which may reduce the size and dimension of members. In addition, the thinner steel plates may help avoid welding problems associated with thick steel plates as reducing the amount of welding work and improving the welding quality. Fatigue damage is one of the most critical service problems of steel bridge structures. There is no special design standard for fatigue performance of high strength steels in the current design code. This paper presents an experimental investigation on fatigue performance of Q690 high strength steels and their welded sections to determine the fatigue strength, so as to promoto the application of Q690 high strength steel in practical engineering. The monotonic tensile tests were carried out on Q690 high strength steels and their welded sections to examine the material properties. The welded section was etched before test to distinguish the position of base metal, heat affected zone and welded metal during testing, and determined the position of necking was heat affected zone. The various applied loadings of fatigue tests were determined according to the mechanical properties examined in the tensile test, and a series of high-cycle-low-strain cyclic tests on smooth cylindrical coupons had been conducted to determine the S-N curves for Q690 high strength steels and their welded sections. The fatigue limit of Q690 welded sections is 420 MPa, and that of base plate is 668. 8 MPa. It means that the fatigue performance of Q690 welded sections is worse than that of Q690 base plate, while the fatigue resistance of both the Q690 base plate and their welded sections are significantly larger than those given in Eurocode (base plate: 118 MPa, welded section: 82.5 MPa). The hardness test was conducted on the Q690 welded section to determine its hardness distribution along the longitudinal direction. It is found that the weld metal exhibits the larger hardness value as 328 HV, while the softening was identified in the heat affected zone with a hardness of 240 HV, which indicated that the hardness distribution of Q690 welded section is uneven and the difference is significant. Based on the results of etching tests and SEM observations on the fracture surfaces under fatigue loadings, it is found that the crack initiated at the fusion zone rather than the heat affected zone. What’s more, non-metallic inclusions have been identified in the fracture surfaces of Q690 welded sections, it means that the initial imperfections may be a critical parameter affecting the fatigue performance of Q690 welded sections.
2024, 39(5): 34-40.
doi: 10.13206/j.gjgS24050105
Abstract:
High strength steel with yield strengths at 690 MPa has been widely used in primary structural members of steel structures because of their strength-to-self-weight ratios. Over the past two decades, there were a number of experimental investigations into mechanical properties as well as structural behaviour of high strength Q690-QT steel welded sections. It is evident now that, these welded sections will suffer from a significant reduction in their mechanical properties, i. e. both yield and tensile strengths as well as ductility, due to change in microstructures if welding is not properly controlled. These experimental investigations focus on describing the structural behaviour of welded sections, and the mechanism of the influence of different welding process parameters on the mechanical properties of high-strength steel welded connections has not been studied. Moreover, the improved welding technology that could avoid the strength reduction of welded high-strength steel could not be proposed. These studied are difficult to provide theoretical evidence for the practical engineering of high-strength steel materials in buildings and bridges. Therefore, a series of carefully planned and executed standard tensile tests were carried out to investigate and quantify effects of various line heat input energy onto the mechanical properties of the Q690-QT steel welded sections. A total of 12 standard tensile tests on cylindrical coupons of welded sections, 3 standard tensile tests on cylindrical coupons of base plate, 3 standard tensile tests on cylindrical coupons of welded metal were conducted, and full range deformation characteristics of these coupons were obtained through use of strain gauges and measurements on high resolution digital images. Both welding methods, namely, GMAW and SAW, were employed to prepare full penetration butt-welded section with various line heat input energy (1. 0, 1. 5, 2. 0, 5. 0 kJ/ mm). It should be noted that GMAW was performed with a robotic welding system while SAW was performed with an automated welding machine to attain high quality welding consistently. After comparison the tested data, the design suggestions for controlling the welded Q690-QT high-strength steel material strength in practical engineering will be proposed. The results show that almost all coupons of the welded sections tested in the present study, fracture occurred within the heat affected zones (HAZ) of the welded sections without any failure in neither the weld metal nor the base plates. For welded sections prepared with a line heat input energy equal to 1.0 or 1.5 kJ/ mm, there were almost no reduction in the mechanical properties of the welded sections. However, for these welded sections prepared with a line heat input energy equal to 2.0 kJ/ mm, only 90% of the yield and the tensile strengths of the base plates was attained. As for these welded sections prepared with a line heat input energy equal to 5.0 kJ/ mm, only 70% of the yield strength of the base plates was attained. Compared with the elongation tested data of base plates and welded sections, the ductility reduction of welded sections is more significant with the increase of heat input energy. Consequently, the effects of welding onto mechanical properties of the Q690 - QT steel welded sections have been successfully quantified, and the information is readily adopted in assessing their mechanical behavior according to various line heat input energy employed during welding. In practical engineering, the equal strength connection of high-strength steel materials could be achieved by setting the heat input energy as 1.0 or 1.5 kJ/mm.
High strength steel with yield strengths at 690 MPa has been widely used in primary structural members of steel structures because of their strength-to-self-weight ratios. Over the past two decades, there were a number of experimental investigations into mechanical properties as well as structural behaviour of high strength Q690-QT steel welded sections. It is evident now that, these welded sections will suffer from a significant reduction in their mechanical properties, i. e. both yield and tensile strengths as well as ductility, due to change in microstructures if welding is not properly controlled. These experimental investigations focus on describing the structural behaviour of welded sections, and the mechanism of the influence of different welding process parameters on the mechanical properties of high-strength steel welded connections has not been studied. Moreover, the improved welding technology that could avoid the strength reduction of welded high-strength steel could not be proposed. These studied are difficult to provide theoretical evidence for the practical engineering of high-strength steel materials in buildings and bridges. Therefore, a series of carefully planned and executed standard tensile tests were carried out to investigate and quantify effects of various line heat input energy onto the mechanical properties of the Q690-QT steel welded sections. A total of 12 standard tensile tests on cylindrical coupons of welded sections, 3 standard tensile tests on cylindrical coupons of base plate, 3 standard tensile tests on cylindrical coupons of welded metal were conducted, and full range deformation characteristics of these coupons were obtained through use of strain gauges and measurements on high resolution digital images. Both welding methods, namely, GMAW and SAW, were employed to prepare full penetration butt-welded section with various line heat input energy (1. 0, 1. 5, 2. 0, 5. 0 kJ/ mm). It should be noted that GMAW was performed with a robotic welding system while SAW was performed with an automated welding machine to attain high quality welding consistently. After comparison the tested data, the design suggestions for controlling the welded Q690-QT high-strength steel material strength in practical engineering will be proposed. The results show that almost all coupons of the welded sections tested in the present study, fracture occurred within the heat affected zones (HAZ) of the welded sections without any failure in neither the weld metal nor the base plates. For welded sections prepared with a line heat input energy equal to 1.0 or 1.5 kJ/ mm, there were almost no reduction in the mechanical properties of the welded sections. However, for these welded sections prepared with a line heat input energy equal to 2.0 kJ/ mm, only 90% of the yield and the tensile strengths of the base plates was attained. As for these welded sections prepared with a line heat input energy equal to 5.0 kJ/ mm, only 70% of the yield strength of the base plates was attained. Compared with the elongation tested data of base plates and welded sections, the ductility reduction of welded sections is more significant with the increase of heat input energy. Consequently, the effects of welding onto mechanical properties of the Q690 - QT steel welded sections have been successfully quantified, and the information is readily adopted in assessing their mechanical behavior according to various line heat input energy employed during welding. In practical engineering, the equal strength connection of high-strength steel materials could be achieved by setting the heat input energy as 1.0 or 1.5 kJ/mm.
2024, 39(5): 41-48.
doi: 10.13206/j.gjgS24050106
Abstract:
Circular concrete-filled steel tubes (CFSTs) can fully utilize the composite action of the steel tube and infilled-concrete, and thus its load-bearing capacity and ductility can be significantly enhanced. Therefore, they are widely used in engineering structures. The application of high-strength steel (HSS) in CFST columns can reduce the size and self-weight of the members and allows structures to achieve greater usable space while saves material, which is more economical and environmentally friendly. However, the current design codes for CFSTs are primarily based on research achievements using ordinary steel strength grades, and whether the codes are still applicable to CFSTs with high-strength steel remains unknown. In addition, existing research on the axial compression behaviour of CFST stub columns with HSS mainly focuses on the structural behaviour at the ultimate load, while little attention is given to the axial force contributions of the steel tube and the infilled concrete at different deformation stages. Therefore, this paper experimentally investigated the axial compression behaviour of CFST stub columns with HSS. Firstly, axial compression tests were conducted on six stub columns, including three CFST columns and three pure steel tubes. The main test parameter was the steel grade, including Q355, Q460, and Q690. Subsequently, based on the test results, the failure states, load-deflections, load-bearing capacity, and axial force contributions of the steel tube and infilled concrete were analysed. Finally, the applicability of the current design codes in predicting the load-bearing capacity of circular stub CFST columns under compression was discussed. The test results indicate that all the pure steel tube and CFST specimens exhibited good ductility. Due to the presence of concrete, the load-bearing capacities of CFST columns were increased by more than 30% compared to these of pure steel tubes. Based on the strain gauges attached on the surface of the steel tube, the axial resistance contributions of the steel tube and infilled concrete of CFST columns were separated. The results show that the confinement provided by the steel tube significantly increased the axial force carried by the concrete, and the increase in concrete axial force was more pronounced with higher steel grades. Although the steel tube provided lateral confinement, its axial force contribution was not significantly reduced compared to its yield load-carrying capacity. Comparative analysis between the experimental results and the predicted results by design codes reveals that the current Chinese design code (GB 50936—2014) can effectively predict the compression resistance of CFST columns using ordinary grade steel, but when high-strength steel is used for the steel tube, the code tends to provide overly conservative or potentially unsafe predictions. The current European design code (EN 1994-1-1) provides reasonable and conservative predictions of the compression resistance for CFST columns using both ordinary steel and high-strength steel. It can still be applied to CFST columns with Q690 HSS. However, EN 1994-1-1 underestimates the axial resistance contribution of the steel tube and overestimates the axial resistance contribution of the infilled concrete.
Circular concrete-filled steel tubes (CFSTs) can fully utilize the composite action of the steel tube and infilled-concrete, and thus its load-bearing capacity and ductility can be significantly enhanced. Therefore, they are widely used in engineering structures. The application of high-strength steel (HSS) in CFST columns can reduce the size and self-weight of the members and allows structures to achieve greater usable space while saves material, which is more economical and environmentally friendly. However, the current design codes for CFSTs are primarily based on research achievements using ordinary steel strength grades, and whether the codes are still applicable to CFSTs with high-strength steel remains unknown. In addition, existing research on the axial compression behaviour of CFST stub columns with HSS mainly focuses on the structural behaviour at the ultimate load, while little attention is given to the axial force contributions of the steel tube and the infilled concrete at different deformation stages. Therefore, this paper experimentally investigated the axial compression behaviour of CFST stub columns with HSS. Firstly, axial compression tests were conducted on six stub columns, including three CFST columns and three pure steel tubes. The main test parameter was the steel grade, including Q355, Q460, and Q690. Subsequently, based on the test results, the failure states, load-deflections, load-bearing capacity, and axial force contributions of the steel tube and infilled concrete were analysed. Finally, the applicability of the current design codes in predicting the load-bearing capacity of circular stub CFST columns under compression was discussed. The test results indicate that all the pure steel tube and CFST specimens exhibited good ductility. Due to the presence of concrete, the load-bearing capacities of CFST columns were increased by more than 30% compared to these of pure steel tubes. Based on the strain gauges attached on the surface of the steel tube, the axial resistance contributions of the steel tube and infilled concrete of CFST columns were separated. The results show that the confinement provided by the steel tube significantly increased the axial force carried by the concrete, and the increase in concrete axial force was more pronounced with higher steel grades. Although the steel tube provided lateral confinement, its axial force contribution was not significantly reduced compared to its yield load-carrying capacity. Comparative analysis between the experimental results and the predicted results by design codes reveals that the current Chinese design code (GB 50936—2014) can effectively predict the compression resistance of CFST columns using ordinary grade steel, but when high-strength steel is used for the steel tube, the code tends to provide overly conservative or potentially unsafe predictions. The current European design code (EN 1994-1-1) provides reasonable and conservative predictions of the compression resistance for CFST columns using both ordinary steel and high-strength steel. It can still be applied to CFST columns with Q690 HSS. However, EN 1994-1-1 underestimates the axial resistance contribution of the steel tube and overestimates the axial resistance contribution of the infilled concrete.
2024, 39(5): 49-56.
doi: 10.13206/j.gjgS24050107
Abstract:
With the development of metallurgical technology, high-strength steel and ultra-high-strength steel with yield strengths of 460 MPa and above have been industrially produced in China, with production increasing year by year. These steels use heat treatment processes to obtain specific microstructural compositions, optimize their material properties and mechanical characteristics, and have outstanding advantages in terms of the stress performance of building structures, economic benefits and energy saving and emission reduction. However, some researchers believe that the microstructures of these high-strength steels are easily affected during the welding process due to the heat treatment process during smelting, resulting in the reduction of various mechanical properties in the weld heat-affected zone. Therefore, there is a great need to study and quantify this post-welding structural behaviour of high-strength Q690 and Q960 steel plates in practical sizes for the construction industry (e. g. 10 to 30 mm thickness). To address this issue, welding process specifications for Q690 and Q960 medium thickness plates were developed, and a comprehensive experimental study was carried out on a total of 36 short columns of high-strength steel to quantify the cross-sectional load carrying capacity of welded spliced short columns of high-strength steels Q690 and Q960 under axial compression with different welding heat inputs, and to analyse, in comparison with the design requirements of the current European Union norm EN 1993-1-1, that the applicability of the existing codes on short columns of high strength steel and ultra-high strength steel is also analyzed, experimental data are povided, and some opinions on the regulations of exising section classification are proposed.
With the development of metallurgical technology, high-strength steel and ultra-high-strength steel with yield strengths of 460 MPa and above have been industrially produced in China, with production increasing year by year. These steels use heat treatment processes to obtain specific microstructural compositions, optimize their material properties and mechanical characteristics, and have outstanding advantages in terms of the stress performance of building structures, economic benefits and energy saving and emission reduction. However, some researchers believe that the microstructures of these high-strength steels are easily affected during the welding process due to the heat treatment process during smelting, resulting in the reduction of various mechanical properties in the weld heat-affected zone. Therefore, there is a great need to study and quantify this post-welding structural behaviour of high-strength Q690 and Q960 steel plates in practical sizes for the construction industry (e. g. 10 to 30 mm thickness). To address this issue, welding process specifications for Q690 and Q960 medium thickness plates were developed, and a comprehensive experimental study was carried out on a total of 36 short columns of high-strength steel to quantify the cross-sectional load carrying capacity of welded spliced short columns of high-strength steels Q690 and Q960 under axial compression with different welding heat inputs, and to analyse, in comparison with the design requirements of the current European Union norm EN 1993-1-1, that the applicability of the existing codes on short columns of high strength steel and ultra-high strength steel is also analyzed, experimental data are povided, and some opinions on the regulations of exising section classification are proposed.
2024, 39(5): 57-63.
doi: 10.13206/j.gjgS24050108
Abstract:
The increasing utilization of high-strength Q690 steel in engineering structures is attributed to its superior strength-to-weight ratio. Understanding the ductile tensile fracture behavior of Q690 steel is crucial for investigating bolted connections between Q690 members. To address this, a comprehensive pilot study was conducted using conventional ductile fracture analysis methods, including the Void Growth Model (VGM) and the Stress Modified Critical Strain (SMCS) model. Through monotonic tensile tests on standard and notched coupons of varying radii, the true stress-strain relationship as well as the plastic fracture strains were directly measured for different triaxiality ratios of Q690 steel. Then the fracture surface of tested coupons was observed under SEM, and the failure mode was distinguished. After analyzing the valleys and plateaus formed by the dimples, and the characteristic length of Q690 steel was calculated, which was used as the mesh size of the subsequent numerical model. Advanced finite element models were then used to calibrate and validate the fracture parameters of VGM and SMCS model by examining the stress state at the fracture initiation point and predicting load-extension characteristics and elongations at fracture. The numerical results revealed that both the VGM and SMCS models failed to provide satisfactory predictions for elongations at fracture in the test coupons, and the prediction error of them reached 31% and 39% respectively. As a result, a modified void growth model was proposed, which considered the influence of stress triaxiality on the fracture strain. Notably, the numerical analysis showed a good agreement between predicted and measured values of elongations at fracture in the tested coupons, and the average prediction error was controlled with 5%. This study highlights the importance of understanding the ductile fracture behavior of Q690 steel and introduces a promising new fracture parameter for improved fracture analysis accuracy.
The increasing utilization of high-strength Q690 steel in engineering structures is attributed to its superior strength-to-weight ratio. Understanding the ductile tensile fracture behavior of Q690 steel is crucial for investigating bolted connections between Q690 members. To address this, a comprehensive pilot study was conducted using conventional ductile fracture analysis methods, including the Void Growth Model (VGM) and the Stress Modified Critical Strain (SMCS) model. Through monotonic tensile tests on standard and notched coupons of varying radii, the true stress-strain relationship as well as the plastic fracture strains were directly measured for different triaxiality ratios of Q690 steel. Then the fracture surface of tested coupons was observed under SEM, and the failure mode was distinguished. After analyzing the valleys and plateaus formed by the dimples, and the characteristic length of Q690 steel was calculated, which was used as the mesh size of the subsequent numerical model. Advanced finite element models were then used to calibrate and validate the fracture parameters of VGM and SMCS model by examining the stress state at the fracture initiation point and predicting load-extension characteristics and elongations at fracture. The numerical results revealed that both the VGM and SMCS models failed to provide satisfactory predictions for elongations at fracture in the test coupons, and the prediction error of them reached 31% and 39% respectively. As a result, a modified void growth model was proposed, which considered the influence of stress triaxiality on the fracture strain. Notably, the numerical analysis showed a good agreement between predicted and measured values of elongations at fracture in the tested coupons, and the average prediction error was controlled with 5%. This study highlights the importance of understanding the ductile fracture behavior of Q690 steel and introduces a promising new fracture parameter for improved fracture analysis accuracy.
2024, 39(5): 64-66.
doi: 10.13206/j.gjg23092020
Abstract:
Three types of flexural-torsional buckling of beams in industrial buildings are introduced, they are girders supporting main beams, beams with purlins on their top flange and beams with fly braces between the lower flange of the steel beam and the purlin. Their elastic buckling moments are given, the differences between them are pointed out, special emphasis is put on the purlin-fly brace and pointing out that it is a type of elastic torsional spring depending on the bending stiffness of the purlins, the buckling moment is directly related to the stiffness of the purlins and thus the traditional concept of lateral braced length is waived.
Three types of flexural-torsional buckling of beams in industrial buildings are introduced, they are girders supporting main beams, beams with purlins on their top flange and beams with fly braces between the lower flange of the steel beam and the purlin. Their elastic buckling moments are given, the differences between them are pointed out, special emphasis is put on the purlin-fly brace and pointing out that it is a type of elastic torsional spring depending on the bending stiffness of the purlins, the buckling moment is directly related to the stiffness of the purlins and thus the traditional concept of lateral braced length is waived.
